Abstract

This study aimed to identify predictive proteomic biomarkers of outcome in women with estrogen and/or progesterone receptor-positive (ER/PR-positive) breast cancer after adjuvant tamoxifen, with sufficient power to alter patient management.

Methods

Using reverse phase protein arrays (RPPA), 140 antibodies were applied to a training set of 197 ER/PR-positive breast cancers to identify predictors. An algorithm was developed that predicted patient outcomes using a subset of antibodies. Since RPPA is a useful exploratory tool but does not lend itself as a practical clinical tool to assay validated biomarkers, quantitative immunofluorescence for selected proteins was applied to 313 ER/PR-positive breast cancers (test set) for validation. Seventy-seven other ER/PR-positive cancers with transcriptional profiling data were used to compare the performance of the proteomic biomarkers and established genomic predictors. All patients were treated with adjuvant tamoxifen after loco-regional therapy.

This study validates proteomic biomarkers that can be assayed in a practical inexpensive manner using immunofluorescence to identify lymph node-negative ER/PR-positive patients with excellent outcomes after adjuvant tamoxifen.